One method to augment the thrust of a turbojet or turbofan engine is to utilize an afterburner. Afterburners increase thrust by adding heat energy to an entering gas stream. Fuel is generally introduced to the gas stream by the afterburner in stages (segments) so that the heat energy can be increased gradually from zero to the desired value. By gradually increasing the heat energy, the afterburner provides increased control and the probability of engine blowout or surge is minimized.
Staging is regulated by a fuel control which inputs fuel to each successive stage in the afterburner so that the mixture ratio in each stage is nearly stoichiometric. Generally, the fuel control has a separate shutoff and pressure regulating valve for each stage. Because there may be sixteen stages, separate shutoff and regulating valves increase both the weight and the volume of a fuel control.